A theoretical and experimental study was made to determine where a fixed length, constant diameter tube should be divided so that when one portion of the tube was used as a gun barrel and the remaining portion was used as a driver, the maximum projectile muzzle velocity would be obtained for a particular driver gas and initial projectile acceleration. Studies were made of several gas gun configurations, of 4-in. (10-cm) inside diameter and 100-ft (30- m) length, for muzzle velocities greater than 500 ft/s (150 m/s). Calculations were made by using the Lagrange theory for very low Mach numbers; the constant diameter, infinite reservoir theory for very high initial accelerations; and the Pidduck-Kent theory for other regimes. Experimental results and theoretical predictions are compared for several gun divisions, helium and nitrogen drivers, and initial accelerations from 200 to 5000 g. For improved gun utilization, gun configurations are suggested to reduce exit gas pressure, to reduce the quantity of driver gas required, and to ease operation and improve (statistical) utilization of the gun without unduly affecting muzzle velocity. Although the results obtained are specific to the Harry Diamond Laboratories 4-in. gas gun, computer programs are included that may be applied to other gun geometries.

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